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Reading Tags using the OPC Web Client ActiveX Controls
Quick links within this page:
Objective
Reading a Single Tag:
In order for our web-page to display anything, we need to tell the server to fetch the Tag value from the OPC Server and then to display it in the page.
 ASP
First, you need to add the following line at the top of the page:
<%@ Language="vbscript" %>
<html>
<head>
<title>OPC Web Client
Example, Single Tag Read from the Web Server</title>
</head>
<body>
<p>The Tag is:
<%
Set opcWebClient = Server.CreateObject("OPCLabs.EasyDA3.0")
Set valueTimeQuality = opcWebClient.ReadItem("", "OPCLabs.KitServer.2", _
& "Trends.Ramp (1 min)")
If Err.Number = 0 Then
Response.Write valueTimeQuality.Value
Else
Response.Write "<font color=red>Error: " & Err.Number & ", " _
& Err.Description & "</font>"
End If
Set valueTimeQuality = Nothing
Set opcWebClient = Nothing
%>
</p>
</body>
</html>
Save your page with a .ASP extension onto your web-server. Now launch your web-browser and connect to your web-page from your web-server. You should see the value of a tag in the page.
ASP.NET
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load 'Put user code to initialize the page here
Try
Dim objOWC As New OPCLabs.EasyOPCDANet.EasyDACOM
Dim objVTQ As VTQ3 = objOWC.ReadItem _
( _
"", _
"OPCLabs.KitServer.2", _
"Simulation.Random") Response.Write("Value:" & objVTQ.Value
_
& "<br>") Response.Write("Qlty:" & objVTQ
.Quality _
& "<br>") Response.Write("Time:" & objVTQ
.TimeStamp _
& "<br>") Catch ex As Exception
Response.Write("Error: " & ex.Message)
End Try
End Sub
Reading to Mulitple Tags:
<%@Language="vbscript"%>
<html>
<head>
<title>OPC Web Client
Example, Reading Multiple Tags</title>
</head>
<body>
<p>Tag is:
<%
Dim EasyDA
Set EasyDA = CreateObject("OPCLabs.EasyDA3.0")
Dim VTQs
VTQs = EasyDA.ReadMultipleItems("", "OPCLabs.KitServer.2", _
Array("Simulation.Random", "Trends.Ramp (1 min)", "Trends.Sine (1 min)", "Simulation.Register_I4"))
Dim strWriteValue
strWriteValue = "Tag Read, data as follows: " & "<br><br>"
Dim I
For I = LBound(VTQs) To UBound(VTQs)
If VarType(VTQs(I)) <> 10 Then
With VTQs(I)
strWriteValue = strWriteValue & "Array Element #" & I & "<br>" _
& "Value: " & .Value & "<br>" _
& "Quality: " & .Quality & "<br>" _
& "Timestamp: " & .TimeStamp
End With
Else
On Error Resume Next
EasyDA.RaiseError VTQs(I)
strWriteValue = strWriteValue & "** " & Err.Source & ": " & Err.Description & " (0x" _
& Hex(Err.Number) & ")" & " **"
On Error Goto 0
End If
strWriteValue = strWriteValue & vbCrLf & "<hr><br>"
Next
Response.Write strWriteValue
%>
</p>
</body>
</html>
ASP.NET
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'Put user code to initialize the page here
Try
'define an opc web client object
Dim EasyDA As New OPCLabs.EasyOPCDANet.EasyDACOM
'define a dictionary to receive the values
Dim VTQs As IDictionary
'Read the items
VTQs = EasyDA.ReadMultipleItems _
( _
"", _
"OPCLabs.KitServer.2", _
New String() _
{ _
"Simulation.Random", _
"Trends.Ramp (1 min)", _
"Trends.Sine (1 min)", _
"
Simulation.Register_I4" _
} _
)
'check if the dictionary contains anything
If Not VTQs Is Nothing Then
'now check if the returned item is an array type
If IsArray(VTQs) Then
'now iterate thru the collection
For Each item As EASYOPCDALib.VTQ In VTQs
'display the item to the browser
Response.Write(item.Value & "<br>")
Next
End If
End If
Catch ex As Exception
Response.Write("Err: " & ex.Message)
End Try
End Sub
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